DNA methylation in adenovirus, adenovirus-transformed cells, and host cells

DNAs of adenovirus type 2 and type 12 contain low amounts of methylated bases (0.01 and 0.02% N6-methyl-adenine per adenine, if any, and 0.04 and 0.06% 5-methylcytosine per cytosine for type 2 and type 12, respectively), whereas the DNA of the mammalian host cells contains much more 5-methylcytosine (3.57% for human KB cells). The DNA of hamster cells transformed by adenovirus type 12 contains 3.11 and 3.14% 5-methycytosine (HA12/7 and T627 cells, respectively), whereas the DNA from untransformed hamster cells (BHK21 cells) contains 2.22% 5-methylcytosine. In the DNA of human and hamster cells, little, if any, N6-methyladenine was detected. Methylation of DNA was determined by a sensitive method based on two consecutive steps of two-dimensional thin-layer chromatography of the radioactively labeled DNA bases. By this procedure the detection limits of 5-methylcytosine and N6-methyladenine could be lowered to 0.01% per main base.